I recommend the novel One Piece: Super Golden Bell Shield to you. The main character was a Heavenly Dragon person who had transmigrated to One Piece's world and became a child. At the same time, he had a golden finger, the supreme ancient martial art Golden Bell Shield that only he could cultivate. When the Merman Race was about to cause trouble, the protagonist had to consider how to use his Golden Bell Shield to resist. I hope you like my recommendation, Mwah ~😗